Different electrical systems or different components with an electrical system operate on analog signals or digital signals. Accordingly, there is an ongoing need to convert digital signals to analog signals and vice versa. In an analog-to-digital converter (ADC) scenario, an analog input signal is sampled, resulting in a representative digital value for each sample. Today, there are many different ADC device topologies and products available with variations in data rate, power consumption, accuracy, resolution, etc.
One type of ADC topology is referred to as a delta-sigma (ΔΣ) topology. In a ΔΣ topology, the input signal is oversampled by a ΔΣ modulator and the output of the ΔΣ modulator is passed through a digital/decimation filter to produce a high-resolution data-stream output. The sampling rate is typically hundreds of times faster than the digital output of the digital/decimation filter. Accordingly, in a ΔΣ topology, individual samples are accumulated over time and “averaged” with the other input-signal samples through the digital/decimation filter.
When an ADC device is included as part of a larger electrical system, the effect of loading by the ADC input on the source needs to be accounted for. In an example electrical system, sensors are employed along with ADC devices to convert analog output signals of the sensors to digital signals for storage and/or analysis. To help ensure an ADC device is compatible with input signals coming from a source with high output impedance (e.g., a scenario where analog output signals from a passive sensor with high output impedance are the input signals to an ADC device), some ADC device topologies include buffers to amplify or otherwise prepare input signals for sampling. Unfortunately, buffer-based ADC device topologies increase ADC cost and layout size. Buffers also increase power consumption and add to the ADC noise. For ADC scenarios involving an input signal with high source impedance, simply removing the buffers is not a workable solution. Efforts to improve ADC design and provide marketable ADC devices are ongoing.